Catheters are used in a variety of procedures to treat vascular maladies throughout the body. Catheters are used to place various treatment materials, drugs, and devices within remote regions of the human body. Catheters with distal balloons are used to treat narrowed regions in the arterial system via percutaneous transdermal angioplasty (PCTA) by expanding the balloon in the region of the plaque narrowing a vessel lumen and pressing the plaque into the vessel wall.
Often, the target which one desires to access by catheter is within a soft tissue such as the liver or brain. Such sites are extremely difficult to reach by way of the vasculature system because the remote arterial pathways are increasingly narrow and have tortuous pathways with sharp bends or curves often winding back on themselves.
Catheters designed to traverse such pathways must provide the desired balance between the flexibility required to allow passage of the catheter tip through the sharp bends of the increasingly narrow blood vessels and the stiffness required to allow sufficient pushability and torqueability as the catheter is inserted into the body and advanced through the tortuous pathways. It is commonplace for modern high performance catheters to have a number of sections of different flexibilities along its length.
In many cases, the catheter is designed to be used as a unit with a torqueable guidewire. The guidewire is typically bent at its distal end and may be guided by rotating and advancing the wire along a tortuous, small vessel pathway, to a target site. The catheter is constructed to slide over the guidewire and traverse the path established by the guidewire. Typically the guidewire and catheter are advanced along the tortuous pathway by alternately advancing the wire along a region of the pathway, then advancing the catheter axially over the advanced wire portion. Further details on the problems and an early, but yet effective, catheter designed for such traversal may be found in U.S. Pat. No. 4,739,768 to Engelson.
One problem that may be encountered as the guidewire and catheter are advanced as described above, is that the guidewire can become stuck or jammed against the internal tubular surface or walls of the lumen. This problem is caused, at least in part, by the distortion of lumen walls against the guidewire, unfavorable friction properties between the guidewire and the lumen surfaces, and/or unfavorable geometrical positioning of the guidewire relative to the inner surfaces of the catheter lumen. Typically, the problem arises when a sharp bend is encountered or where two or more sharp bends occur in succession. When the catheter and wire become locked together in this manner it may be impossible to either advance or withdraw the wire relative to the catheter. In such cases, the wire and catheter must be withdrawn together until both are straight enough to allow the wire to be moved freely axially within the catheter, and often, it may not then be possible to reach the targeted site. This same problem may be encountered when other types of instruments (i.e., an angioscope) is advanced through a catheter lumen.
In a number or procedures, it may be necessary that the catheter have two or more lumens extending within at least a portion of the catheter shaft. For example, the catheter may have one lumen adapted for use with a guidewire to position the catheter, and one or more additional lumen for balloon inflation or deflation, irrigation, delivery of drugs or other treatments, or to facilitate the insertion of other surgical devices, such as for example, an angioscope. The lumen employed may have any suitable cross-sectional shape as required for the particular use.
Such multilumen catheter designs are particularly susceptible to kinking or ovalization of the cross-sectional shapes of the various lumen when the catheter is exposed to high flexure or high torsion, such as when the catheter is traversed through the bends in the vasculature. While a certain small amount of distortion of the interior cross-sectional shapes of a lumen may be acceptable in some applications, such distortions of the interior shapes of the lumen may result in a lumen being kinked or closed off or may result in the wall of the lumen being forced against any element that has been inserted into the lumen as described above. For example, ovalization of a normally round shaped guidewire lumen causes the lumen walls to pinch the guidewire thus prohibiting free relative movement between the guidewire and the guidewire lumen. Multilumen catheters known in the art do not tend to provide a suitable shaft design to ensure the free relative movement of an element (i.e., a guidewire) placed within a guidewire lumen.
While some of these disadvantages may be somewhat alleviated by increasing the thickness of the catheter lumen walls, it is not desirable to do so for a number of reasons. Increased wall thickness may adversely decrease flexibility, increase the overall size of the catheter profile, or decrease the internal space available for necessary lumens. In addition, increased wall thicknesses typically result in increased mass. Increased mass increases the tendency of the catheter to force the guidewire out of a bent or curved configuration as the catheter is advanced over the guidewire. This may be critical in the distal tip region of some over-the-wire catheters because a relatively low mass at the distal tip region of the catheter may be necessary for tracking the catheter over the increasing flexible guidewires necessary to access the more tortuous vascular pathways.
To some extent, the problem of catheter collapse has been addressed in multilumen hemodialysis catheter designs using a reinforced construction. For example, U.S. Pat. 5,190,520 to Fenton, Jr. et al. discloses a reinforced dual lumen catheter having a cylindrical portion with a central axis and a substantially rectangular divider within the cylindrical portion which defines two internal D-shaped lumens. A wire reinforcement filament is embedded in the cylindrical portion in a helical pattern about the central axis. The reinforced multilumen catheter disclosed in U.S. Pat. No. 5,221,255 to Mahurkar et al. discloses similar cylindrical tube having a septum extending therein which defines two D-shaped lumens. To minimize kinking the catheter has a spiral of relatively stiff material embedded in the cylindrical wall of the catheter which tends to hold the outer wall of the catheter in a cylindrical shape. The catheter further has a reinforcing member extending along the full length of at least one of the lumens, preferably the reinforcing member is embedded in the septum.
An extrusion method for producing a reinforced multilumen tubing is disclosed in U.S. Pat. No. 5,063,018 to Fontirroche et al. The disclosed extrusion method involves first extruding an inner tube over a wire mandrel, adding a braided tube if desired, and then extruding an outer tube over the inner braided tube. The wire mandrel forms a first lumen within the braided tube and a second lumen is formed in the outer tube during extrusion. Of course, the resulting tubing construction is limited to materials which are suitable for extrusion and to tubing sizes and thicknesses obtainable by the extrusion process.
None of these constructions, however, provide a low-profile, high flexibility catheter shaft having a reinforced lumen which resists cross-sectional distortion and provides for free axial movement of an inserted element relative to the lumen as the catheter device is advanced through the curves and sharp bends of a vascular pathway as described in detail below. Further, none of these devices have a reinforced lumen having a low profile, low mass, low friction construction as described below.